This session focuses on the influence of CO2, temperature, water stress, and nutrients on ecosystem functioning and structure. A focus is set on learning from manipulative experiments and novel uses of continuous ecosystem monitoring and Earth observation data for informing theory and ecosystem models. Contributions may cover a range of scales and scopes, including plant ecophysiology, soil organic matter dynamics, soil microbial activity, nutrient cycling, plant-soil interactions, or ecosystem dynamics.
Temperature anomalies, such as heatwaves and cold spells, are becoming increasingly common, posing significant challenges to ecosystem functioning and carbon sequestration. While temperature anomalies have been shown to influence broad-scale carbon flux patterns, their fine-scale effects, particularly in conjunction with agricultural management, remain poorly understood. This study investigates the impact of air temperature (Tair) anomalies on CO₂ fluxes in an upland mesic grassland under two grazing management regimes: low cattle grazing intensity and high cattle grazing intensity and fertilisation. Using 18 years (2003–2021) of CO₂ flux and climate data, we assessed gross primary productivity (GPP) and ecosystem respiration (Reco) responses to temperature anomalies, including cold, warm, extreme cold, and extreme warm conditions. The study site experienced an average of 40 anomalous temperature days per year, including ~10 days of extreme events. CO₂ fluxes were most affected by temperature anomalies during the early growing season, with the strongest increases in GPP and Reco observed in spring. Warm anomalies generally enhanced CO₂ fluxes in spring but suppressed them in summer and autumn, particularly under extreme warm conditions lasting more than six days. This suppression likely reflects the exceedance of a temperature stress threshold (~20°C). Management intensity modulated these responses. High-intensity grazing and fertilisation increased the sensitivity of CO₂ fluxes to warm anomalies, whereas low-intensity grazing appeared to buffer fluxes against temperature-induced stress. Cold anomalies promoted asynchrony between patterns of grassland carbon uptake and release, adding further complexity to temperature–flux relationships. Our findings emphasize the importance of management × climate interactions in shaping CO₂ flux responses. Low-intensity management regimes may enhance ecosystem resilience to warming in cool temperate grasslands, providing a potential adaptation strategy under climate change. This study highlights the importance of long-term, field-based research to refine our understanding of how grasslands can maintain their carbon sink capacity amidst increasing temperature extremes.
How to cite: Klumpp, K., Bloor, J. M. G., and Winck, B.: Effects of management and temperature anomalies on grassland CO2 fluxes using a long-term eddy covariance dataset , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11206, https://doi.org/10.5194/egusphere-egu25-11206, 2025.
An accurate understanding of the plant-soil biogeochemical cycles is crucial to model the impacts of global change. However, further exploration is needed to disentangle the role of microbes in plant carbon and nitrogen uptake under warming and drought. In this study we perform a manipulative experiment increasing temperature and water deficit in 240 pots, considering six different grassland species (2 forbs, 2 grasses, and 2 N-fixers) and two different soil types (coming from intensive and extensive managing practices). By analyzing N content, N labeling, and biomass production in the soil, microbial, belowground, and aboveground compartments we study potential interactions between the plant-microbial-soil system in different conditions. Preliminary results indicate that water availability is more important than warming to regulate biomass production and nutrient uptake. In addition, N availability determines the interaction between plants and the microbial community. These findings will help better incorporate the role of microbes in nutrient cycling and better understand the impacts of future conditions, anticipated to be warmer and dryer.
How to cite: Vallicrosa, H., Mariotte, P., and Grossiord, C.: The role of plant-soil-microbe interactions on nitrogen cycling under drought and warming in grasslands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2870, https://doi.org/10.5194/egusphere-egu25-2870, 2025.
Soils at high latitudes are experiencing significant warming due to climate change, raising concerns about potential disruptions in nitrogen (N) and carbon (C) cycling. This study investigates the decadal effects of soil warming on microbial N transformations in an Icelandic grassland. To this purpose, a geothermal gradient was utilized, where soil temperatures varied naturally from +0ºC to +12.3°C, simulating enhanced warming effects. Seasonal sampling of N pools and rates of gross N transformations—including amino acid, ammonia, and nitrate consumption and production—provided insights into microbial responses to prolonged warming.
Warming accelerated the turnover of amino acids, driven by increased rates of microbial production and consumption, but did not affect net protein depolymerization. Ammonia consumption rates increased with temperature, although production rates remained constant. Additionally, total soil N content decreased substantially after five years of warming but remained stable between 5 and 10 years of warming. These findings suggest that N losses induced by warming occurred primarily within the first five years, stabilizing in a new equilibrium without further N losses. The enhanced microbial C limitation in warmed soils likely compelled microorganisms to rely more on the turnover of organic N pools as a dual source of both C and N to meet their heightened metabolic demands, thus preventing further N losses.
Overall, these findings challenge the assumption of progressive N depletion under warming conditions and highlight the role of microbial physiological adaptations in maintaining soil N availability despite increased metabolic demands.
How to cite: Zevenhuizen Martínez, A. L., Richter, A., Fuchslueger, L., Prommer, J., Verbrigghe, N., Peñuelas, J., Sigurdsson, B. D., and Marañón-Jiménez, S.: Nitrogen dynamics and Microbial Adaptations in High-Latitude soils under Decadal Warming, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3654, https://doi.org/10.5194/egusphere-egu25-3654, 2025.
Nitrogen (N) fixation by cyanobacteria on mosses is a critical N source, particularly in moss-abundant and pristine ecosystems such as boreal forests, where it is estimated to contribute over 50% of total ecosystem N input. However, the upscaling of these field estimates in N fixation carries considerable uncertainty because they rely on point sampling of a limited number of species, which fails to capture the potential large spatial and temporal variation in N fixation. As a result, the global spatial pattern of moss-associated N fixation remains poorly understood, limiting the assessment of its relative importance at the global scale. Additionally, modeling global N fixation rates is constrained by the lack of a comprehensive understanding of how moss-associated N fixation relates to the full range of key abiotic drivers across diverse climate zones.
To address these uncertainties, we measured the response of N fixation rates in 2-3 dominant moss species across five climate zones (arctic, boreal, temperate, mediterranean, and tropical) to a full range of key abiotic drivers (i.e., water content, surface temperature, and incident light intensity). By identifying the key parameters of each response curve, we integrated the N fixation process into the process-based model LiBry. We then applied this extended LiBry model to simulate the global pattern of N fixation and assess its relative importance across climate zones.
Our results reveal that different species within the same climate zones exhibit similar response curves to light, water, and temperature, with comparable optimum values for temperature, light, and water content. Moreover, the optimum temperature (~27 °C) and water content (~100%) remain consistent not only across species but also across climate zones, regardless of variations in local temperature and humidity conditions, while the optimum light intensity varied among climate zones. However, moss-associated N fixation rates were higher in boreal, tundra, and mediterranean habitats compared to tropical lowlands and temperate regions. These results indicate that the responses of N fixation to temperature, light, and water content show little species specificity, and further, optimum temperature and water content were unaffected by sample origin (climate).
Our study provides the first global assessment of N fixation in moss-cyanobacteria associations, highlighting variation across climate zones. Our results also stress the need for ecosystem models to incorporate moss-associated N fixation as an essential component of total ecosystem N input, especially in unpolluted systems such as boreal and mediterranean forests and arctic tundra.
How to cite: Ma, Y., Porada, P., and Rousk, K.: Global nitrogen fixation patterns in moss-cyanobacteria associations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-239, https://doi.org/10.5194/egusphere-egu25-239, 2025.
Vegetation leaf phenology (i.e. the timing of leaf onset and offset) determines the temporal bounds of the growing season. Thereby leaf phenology strongly influences the exchanges of energy and CO2 between the atmosphere and the biosphere. However, accurate parameterization of leaf phenology processes in terrestrial biosphere models is challenging due to a poor understanding of the physical drivers of leaf recovery and senescence and their co-variance in space. Vegetation phenology in Northern Hemisphere permafrost regions is affected by more complex permafrost processes compared with the other terrestrial ecosystems. Yet the heterogeneity of vegetation response within permafrost regions is often overlooked in global simulations that treat the region as a whole. Further, PFT-based biogeochemistry models set phenological parameters as simply constants, but do not take into account the vegetation heterogeneity within the same plant functional type.
Here, we derive optimal heat-related phenological parameters within the QUINCY model by inversing remote sensing information. Compared to the model’s default parameters, these optimized parameters significantly improve the prediction of the growing season start and ending in more than 70% and 80% of Northern Hemisphere permafrost regions, respectively. Our results reveal significant variability in vegetation phenological responses across different permafrost regions covered by herbaceaous vegetation types. This suggests that phenological parameters in terrestrial biosphere models must be tailored to local environmental conditions. This implication is further verified by QUINCY model. This study provides insights into the potential for enhancing model performance with the help of remote sensing information, and emphasizes the necessity for local parameterization across different ecosystems within Northern Hemisphere permafrost regions by terrestrial biosphere models.
How to cite: Zhu, Y., Lacroix, F., and Zaehle, S.: Optimizing phenological parameters for bridging remote sensing and QUINCY model in permafrost regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13578, https://doi.org/10.5194/egusphere-egu25-13578, 2025.
The response of photosynthesis to temperature and CO₂ remains poorly represented in land surface models, contributing to significant uncertainty in land carbon sink estimates. Here, we incorporate photosynthetic capacity adaptation and acclimation to temperature into the JULES land surface model, and we investigate the sensitivity of photosynthesis to CO₂ acclimation. Using an RCP8.5 climate scenario, we quantify the impact of these processes on Gross Primary Productivity (GPP). Simulations accounting for adaptation and acclimation to temperature and CO2 increases modelled global GPP by 2050. Temperature acclimation in the extra tropics enhances GPP, but adaptation in the tropics weakens the CO2 fertilisation response decreasing GPP. CO2 acclimation down-regulates photosynthetic capacity, causing a universal decline in the rate of GPP enhancement across biomes. Our findings emphasize the need for models to incorporate temperature adaptation and acclimation to avoid underestimating global carbon uptake and to better capture spatial variability in responses to rising temperatures. In addition, improving our understanding of CO₂ acclimation across biomes and its integration into models is critical for reducing uncertainties in future carbon cycle predictions.
How to cite: Oliver, R., Mercado, L., Medlyn, B., Harris, P., and Clark, D.: Impacts of photosynthetic capacity acclimation and adaptation to temperature and CO2, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2522, https://doi.org/10.5194/egusphere-egu25-2522, 2025.
Tree roots adapt their morphological, physiological and biochemical functional traits to optimise nutrient acquisition, notably in response to global changes. Therefore, it is hypothesized that, to increase nutrient acquisition under elevated CO2 (eCO2) to sustain productivity, trees will allocate more carbon assimilates into their root systems. As fine roots are thought to represent ~1/3 of global NPP, understanding how much of the additional carbon (C) introduced into the forest ecosystem by increased photosynthesis is allocated belowground, will improve the accuracy of coupled biosphere-atmosphere models and our understanding of future global C budgets.
We assess the effect of eCO2 on the biomass, morphology, depth distribution and turnover of fine roots of 180-year-old English Oak trees in years 4-7 of an ongoing study (2017-2031) at the Birmingham Institute of Forest Research free air carbon dioxide enrichment (BIFoR FACE) experiment. BIFoR FACE is currently the only experiment in a mature temperate forest simulating the CO2 concentrations predicted to be the 2050 planetary norm (+150ppm above ambient). For ambient and eCO2 treatments, 1-metre soil cores were used to assess fine root standing stock, morphology (length, diameter and specific root length (SRL)) and depth distribution. A minirhizotron camera was used to assess fine root production, mortality and turnover across 2 years.
There was >40% more fine root biomass under eCO2 in all depth profiles down to 50cm, driven by an increase in fine root length. This displays how more carbon assimilates were allocated to the fine root systems of this mature, temperate forest under eCO2. Below 50cm the roots were longer and thinner under eCO2, showing how an increase in the available surface area of the root system for nutrient uptake is achieved through a shift in morphology alongside an increase in standing stock. Contrary to our expectation, the distribution of fine root biomass did not shift to greater depths under eCO2. Long-term minirhizotron data shows strong seasonal cycles in fine root production and mortality, modulated by eCO2.
How to cite: Handy, G., Arnaud, M., Esquivel-Muelbert, A., Carter, I., Kourmouli, A., Mayoral, C., and Mackenzie, A. R.: Changed Root Dynamics in a Mature Temperate Forest Under Elevated CO2, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17161, https://doi.org/10.5194/egusphere-egu25-17161, 2025.
Terrestrial ecosystem respiration (TER) is the second largest CO2 flux between biosphere and atmosphere after photosynthesis. It is therefore crucial to understand the dynamics and drivers of TER to be able to accurately model the net CO2 exchange between biosphere and atmosphere under a changing climate. Most studies focus on the temperature dependence of TER. However, precipitation and soil moisture can also have a major impact on TER, especially in arid environments. Disentangling the impacts of temperature and soil water on TER is an important challenge to reduce uncertainties in modelling the carbon cycle and its climate change feedbacks.
Here we use daily nighttime net ecosystem exchange (NEE) data as proxy for TER collected by more than 30 flux tower stations within the OzFlux network over the last 20 years in Australia. These stations cover a broad range of climate conditions enabling us to analyze the dependence of TER on soil moisture under varying aridity conditions. We find that the sensitivity of TER to soil moisture variability is much stronger in semi-arid regions than in arid or humid areas. For the most arid stations, soil respiration is in general limited by the small amount of available litter substrate. Soil respiration fluxes at humid stations, however, are large but show only low or even negative sensitivity to the high soil moisture levels indicating that TER at humid stations is not water-limited. We show that common model approaches assuming a constant TER sensitivity for all soil moisture levels fail in reproducing the observed TER behavior in Australia. Hence a more sophisticated description of TER with respect to its soil moisture dependence is necessary to capture TER dynamics under different climate conditions accurately.
How to cite: Metz, E.-M., Vardag, S. N., Feldman, A. F., Poulter, B., and Butz, A.: Sensitivity of Terrestrial Ecosystem Respiration to Soil Moisture Under Different Aridity Conditions in Australia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9595, https://doi.org/10.5194/egusphere-egu25-9595, 2025.
Anthropogenically-induced climate change is rapidly altering Earth’s carbon cycles. However, information on long-term and large-scale responses of soil respiration—a key process releasing CO₂—remains limited. Soil CO₂ production, driven by rhizosphere and microbial respiratory activity, is inherently temperature sensitive. Yet, thermal adaptation, substrate depletion and other constraints such as drought may dampen responses to climate warming. Assessing soil respiration at broader temporal and spatial scales is hampered by its high variability and the labor-intensive nature of CO₂ flux measurements. Consequently, evidence for longer-term enhancement of soil respiration in response to ongoing climatic warming remains scarce.
Here, we analyze 50-year long records of dissolved inorganic carbon (DIC) from Swiss rivers draining Alpine catchments to infer long-term and large-scale responses of soil CO₂ production. Riverine DIC flux originates from CO₂ dissolved in water, with approximately half derived from belowground respiratory activity and the remainder released through weathering processes. Our radiocarbon and stable isotope analyses confirm these sources in Swiss rivers.
Long-term records from the Swiss national river surveillance program reveal that average DIC concentrations in rivers draining the Swiss Alps (Rhine, Inn, Ticino) have increased by 1.6% per decade since the 1980s. This decadal-scale rise in DIC concentrations correlated significantly with the increase in water temperatures by approximately 1.3°C in this period. The DIC increase is not linked to multi-annual variations in river discharge, which drive interannual variability. Analyzing the relationship between discharge and DIC concentrations shows that, for a given discharge, DIC concentrations in the Rhine, Inn, and Ticino have increased in recent decades compared to levels observed in the 1980s and 1990s.
Export of DIC by Swiss rivers only accounts for approximately 2% of the CO2 released from Swiss ecosystems. Nevertheless, the decadal-scale increase in DIC indicates that CO2 production in the soil must have increased. The DIC increase occurred despite a decreasing CO₂ solubility with rising water temperatures. Linking the observed DIC increase to the warming of 0.35°C per decade yields a temperature dependency (Q₁₀) of 2.2. This aligns with values from annual monitoring efforts and short-term soil warming studies across Swiss ecosystems, ranging between 2.3 and 5.3. Our finding indicates a sustained, large-scale stimulation of soil respiration in Alpine environments driven by climate warming, with little thermal adaptation over decadal timescales.
How to cite: Hagedorn, F., Rhyner, T., Storck, F., Brunmayr, A., Flury, R., Minich, L., Zobrist, J., and Eglinton, T.: Rising dissolved inorganic carbon in Alpine rivers evidence enhanced soil respiration driven by climatic warming over the past decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17792, https://doi.org/10.5194/egusphere-egu25-17792, 2025.
Climate change, increasing storms, and sea level rise are increasingly affecting coastal forest ecophysiology and mortality, leading to widespread ‘ghost forests’ and marsh incursion. However, it is difficult to predict the rapid changes observed at these terrestrial-aquatic interfaces as the complex interplay of hydrological, ecological, biogeochemical, and physiological responses driving ecosystem stress and change is not well understood. We describe TEMPEST, a unique manipulative experiment to simulate extreme freshwater and estuarine-water disturbance events over multiple years in 2000 m2 plots. This experiment was implemented in a deciduous coastal US forest with no known prior exposure to seawater. A dense network of environmental, soil, and tree sensors captured the cascading effects of each of the three annual flood treatments—300 m3 or 15 cm water per day per plot—with sensor data streaming in real time to project scientists and then openly available for community analysis.
The first TEMPEST event in 2022 significantly but temporarily impacted the system’s hydrology, with more subtle influences on biogeochemical, soil gas flux, and vegetation components. Pedological changes and vegetation stress built rapidly in subsequent years, however, and by years two and three sap flow rates in three deciduous tree species were disproportionately and negatively affected in the saltwater plot: growing season sap flux of tulip poplars was 25% lower than in the control plot, with the trees exhibiting canopy loss. Maple and beech were also negatively affected but to a lesser extent. The novel TEMPEST experiment provides insight into how the impacts of storm surges accumulate in upland coastal ecosystems’ soils and vegetation, explores the relative influence of flooding and salinity on the magnitude of change, and will be a crucial reference to improve our models of understudied coastal ecosystems.
How to cite: Bond-Lamberty, B., Doro, K., Hopple, A., McDowell, N., Morris, K., Myers-Pigg, A., Pennington, S., Phillips, E., Regier, P., Srinivasan, R., Stearns, A., Ward, N., Bailey, V., and Megonigal, J. P.: An ecosystem-scale flooding experiment to disentangle mechanisms of coastal forest resilience and vulnerability to extreme flooding events , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14277, https://doi.org/10.5194/egusphere-egu25-14277, 2025.
Terrestrial biodiversity in Antarctica is low compared to most temperate and tropical systems, resulting in nutrient-limited ecosystems characterised by low complexity. The establishment of a single non-native species can profoundly disrupt these ecosystems. One such species is the flightless midge, Eretmoptera murphyi (Diptera: Chironomidae), a fly with soil-dwelling detritivorous larvae that was accidentally introduced to Signy Island (South Orkney Islands, maritime Antarctic) from its native South Georgia (South Sandwich Islands, sub-Antarctica) in the 1960s. The fly now occurs with an overall biomass exceeding that of all native microarthropod species combined in some areas of the island. Studies have shown that high larval densities are associated with significant increases in soil nitrate concentrations, potentially impacting native flora and fauna and creating favourable conditions for further invasions by non-native species.
This study investigated the influence of E. murphyi presence on a broader range of soil biogeochemical properties, utilising advanced biochemical methods to measure nitrate, ammonia, phosphorus, total nitrogen and total carbon content. The results indicate that Signy Island soils inhabited by the fly have high organic content (~32% carbon) and are acidic (pH ~4.5). Soils colonised by E. murphyi exhibited significantly higher concentrations of nitrate and ammonia compared to control sites, while phosphate levels showed no significant difference, likely due to the acidic substrate.
The potential future impact of E. murphyi presence and climate change on greenhouse gas emissions from these soils was explored through incubation experiments. Over three-month incubations, elevated temperatures representing medium (9°C) and high (14°C) future warming scenarios increased emissions of nitrous oxide (N₂O) and carbon dioxide (CO₂) from the soils, compared to the current annual average temperature (4°C). Soils from E. murphyi-occupied sites released significantly more N₂O and CO₂ than control soils, possibly due to increased microbial activity. This may be due in part to the higher water content in E. murphyi soils, which may increase microbial abundance and activity. Methane (CH₄) emissions decreased over time in all scenarios, suggesting a shift in microbial community composition.
We suggest it is possible that E. murphyi increases microbial biomass through the introduction of its non-native microbiome, resulting in increased microbial respiration rates and, thereby, amplifying greenhouse gas emissions from Antarctic soils as temperatures rise. Notably, the observed increase in N₂O emissions suggests that E. murphyi may introduce or promote the activity of microorganisms capable of ammonia oxidation, a suggestion supported by parallel microbiome studies. In a separate study of E. murphyi’s microbiome, we confirmed the presence of archaea and bacteria known to carry out ammonia oxidation and other N₂O-producing processes, such as denitrification. Key taxa identified include Crenarchaeota, Actinobacteria, Chloroflexi, and Proteobacteria. Collectively, these findings emphasise the potential for E. murphyi to significantly alter Antarctic soil processes and contribute to climate change-driven feedback loops in these polar ecosystems.
How to cite: Brayley, O., Convey, P., Ullah, S., and Hayward, S.: The effects of a non-native insect on Antarctic soil biogeochemistry and potential greenhouse gas emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13195, https://doi.org/10.5194/egusphere-egu25-13195, 2025.
In the short- or mid-term, the variation of leaf-respired δ13CO2 has important consequences for δ13C of CO2 in air in terrestrial ecosystems. Therefore, the isotope composition of plant respired CO2 is of crucial importance for understanding plant and ecosystem carbon balance. It has previously been shown in tobacco (Nicotiana tabacum) that the balance between ammonium and nitrate has an influence on δ13C of leaf-respired CO2. However, uncertainty remains as to whether (i) the effect of N nutrition is observed in all species, (ii) N source also impacts on respired CO2 in roots, and (iii) there is a relationship or equation predicting δ13C of respired CO2 that can be applied regardless of N conditions and species, this uncertainty represents a hurdle in plant 13C budget modelling.
Here, we carried out isotopic measurements of respired CO2 and various metabolites using two species (spinach, French bean) grown under different NH4+:NO3- ratios. Both species showed a similar pattern, with a progressive 13C-depletion in leaf respired CO2 as the ammonium proportion increased, while δ13C in root-respired CO2 showed little change. Supervised multivariate analysis showed that δ13C in respired CO2 was mostly determined by organic acid (malate, citrate) metabolism, in both leaves and roots. We then took advantage of non-stationary, two-pool modelling that explained 73% of variance in δ13C in respired CO2. It demonstrates the critical role of the balance between the utilization of respiratory intermediates and the remobilization of stored organic acids, regardless of anaplerotic bicarbonate fixation by phosphoenolpyruvate carboxylase and the organ considered.
How to cite: Xia, Y., Lalande, J., Badeck, F., Girardin, C., Bathellier, C., Gleixner, G., Werner, R., Ghiasi, S., Fresneau, C., Tcherkez, G., and Ghashghaie, J.: Nitrogen nutrition effects on δ13C of plant respired CO2 are mostly caused by concurrent changes in organic acid utilization and remobilization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15554, https://doi.org/10.5194/egusphere-egu25-15554, 2025.
Hydraulic activation of stomata (HAS) is the process of wicking water from the leaf interior to the surface, promoted by deliquescent salt on the leaf surface, serving as a critical physiological mechanism that affects stomatal behavior, water fluxes, and ultimately water use efficiency (WUE) in vegetation. This study is the first to evaluate the HAS effect under field conditions, investigating the potential role of hygroscopic urea ammonium nitrate (UAN) foliar application promoting HAS and detecting its effects through changes in transpiration, stomatal slope (g1), carbon-water exchange rate (λ), and inherent water use efficiency (IWUE) at the ecosystem scale.
Using eddy covariance (EC) observations across four ICOS European cropland sites (FR-Gri, BE-Lon, DE-Kli, DE-Geb) from 2005 to 2020, our findings revealed distinct crop-specific responses, with HAS influencing transpiration dynamics after foliar UAN application. Barley, maize, and winter wheat exhibited significantly increased transpiration, as evidenced by substantial increases in g1 and λ (p < 0.05). These changes were accompanied by reductions in IWUE, reflecting enhanced stomatal conductance and more water loss under the HAS effect. In contrast, rapeseed showed reductions in transpiration, g1, and λ, but an increase in IWUE, suggesting improved water use efficiency through distinct physiological response. Except for rapeseed, foliar UAN application enhanced CO2 assimilation, leading to a larger difference in CO2 concentrations (Ca − Cs) and decreased temperature gradient (Ta − Ts) between air and surface, which was attributed to cooling effects induced by elevated transpiration across sites. Notably, g1 remained stable over a one-month period in the absence of foliar UAN application, indicating that observed changes in WUE are primarily driven by the effects of UAN rather than intrinsic stomatal regulation under natural growth conditions.
These findings highlight HAS’s distinct impacts on transpiration, surface energy fluxes, and WUE under field conditions, underscoring the need to incorporate HAS into ecosystem models. The neglect of HAS in current models results in an overestimation of WUE following foliar fertilization in cereals. This limitation may also extend to other vegetation types due to hygroscopic deposition of aerosols, emphasizing the broader significance of integrating HAS into models to improve WUE predictions and support sustainable ecosystem management practices.
How to cite: Deng, S., Burkhardt, J., Lauerwald, R., Flechard, C., Knauer, J., Kalalian, C., Dumont, B., Viovy, N., and Loubet, B.: Detection of the effects of hydraulic activation of stomata (HAS) on the water use efficiency of crops, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4478, https://doi.org/10.5194/egusphere-egu25-4478, 2025.
To address the key question of how future climate change will affect terrestrial ecosystems in terms of biogeochemical cycles, we propose a model framework integrating multi-source observations and global carbon-nitrogen cycle models. This allows us to explore the response patterns of carbon and nitrogen fluxes in global forests, grasslands, and croplands under elevated atmospheric carbon dioxide (CO2), warming, and altered precipitation regimes.
We find that elevated CO2 generally benefits terrestrial ecosystems by enhancing carbon and nitrogen cycling, leading to increased productivity and reduced nitrogen loss. On the other hand, warming and altered precipitation tend to exacerbate inequalities in global carbon and nitrogen cycles, widening the development gap between the Global South and North.
Understanding these biogeochemical feedbacks under climate change is crucial for guiding effective adaptation and mitigation strategies, which are essential for maintaining the health of terrestrial ecosystems and the planet as a whole.
How to cite: Cui, J. and Gu, B.: Impacts of Climate Change on Terrestrial Carbon and Nitrogen Cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2441, https://doi.org/10.5194/egusphere-egu25-2441, 2025.
Remote sensing-based global carbon flux and water products have gained worldwide prominence due to their feasibility to capture spatial patterns, interannual variability and long-term trend of ecosystem carbon and water dynamics from landscape to global scales. The Breathing Earth System Simulator (BESS), a sophisticated coupled process-based diagnostic terrestrial model, integrates multiple physical and bio-geological processes, including atmospheric transfer, canopy radiative transfer, and soil system. BESS has demonstrated robust performance across temporal and spatial scales from 1982 to 2019 when equipped with MODIS Atmosphere and Land products. This study aims to produce global gross primary productivity (GPP) and evapotranspiration (ET) products from 2018 to 2024 using the BESS model, utilizing datasets such as land surface temperature (LST), albedo, leaf area index (LAI), and shortwave radiation (SWR) from the GCOM-C SGLI satellite. Operated by JAXA, Japan, GCOM-C SGLI provides medium spatial resolution (250 m to 1 km) and an 8-day temporal resolution, offering improved sensor stability compared to BESS’s default inputs from MODIS datasets. The main results of this study are: (1) The initial GPP and ET outputs showed fine showed fine linear relations with measurements of GPP (R2 = 0.56), and ET (R2 = 0.45) from 300 collected global flux sites from Fluxnet Ameriflux, Ozflux, Asiaflux; (2) Interannual variations from in response to climate extremes were captured, such as the 2020 Russian heatwave and the 2022 extreme dry summer in southwestern China. (3) From a sensitivity analysis of 21 BESS input parameters, 8 were selected and optimized using the Distributed Alternating Direction Method of Multipliers (D-ADMM), resulting in improved performance with GPP (R² = 0.81) and ET (R² = 0.72). Our GPP and ET products (250m and 1km) will be soon released on the JAXA website, aiming to improve better understanding of global climate and carbon cycle changes.
How to cite: Shao, S., Hase, M., and Ichii, K.: The Development of Global GPP and ET Products of Enhanced BESS Model Derived from GCOM-C SGLI Datasets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14369, https://doi.org/10.5194/egusphere-egu25-14369, 2025.
Airborne and ground-based measurements have consistently shown a rise in the seasonal amplitude of atmospheric CO2 concentration since the 1960s, particularly notable in the high northern latitudes. For instance, Barrow (BRW, 71ºN) witnessed a 50% increase in CO2 amplitude from 1960 to 2011, compared to a 15% increase at Mauna Loa (MLO, 20ºN). This trend suggests significant alterations in biosphere-atmosphere interactions and a changing carbon cycle in northern ecosystems. Previous studies suggest that the enhanced amplitude of atmospheric CO2 is mainly caused by the amplified plant productivity in northern ecosystems. However, the major factors that drive the increasing CO2 amplitude in the northern ecosystems are still subjected to debate, reflecting the fact that the underlying mechanisms or processes that govern the changes still remain unclear. Our study aims to understand these changes from both modelling and observational perspectives by using long-term (1980-2018) monthly CO2 concentration records, incorporating climate data, land cover changes, fire emissions, and ecosystem carbon fluxes (including gross primary production and ecosystem respiration). In parallel, we employed the LPJmL dynamic global vegetation model coupled with the TM3 atmospheric transport model (LPJmL+TM3) to simulate the seasonal CO2 concentration shifts and investigate the cause of the increasing CO2 amplitude. Our results show that the LPJmL+TM3 successfully captures both the interannual variability and the rising trend in CO2 amplitude from 1980 to 2018. We assessed the impact of various factors on CO2 amplitude changes. Our results suggest that the inter-annual variability of gross primary production plays an important role in the rising trend of CO2 amplitude. Further analysis shows that the long-term CO2 amplitude trend is a result of the combined effect of vegetation and climate change.
How to cite: Fan, N. and Forkel, M.: Drivers of the enhanced amplitude of atmospheric CO2 in northern terrestrial ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7279, https://doi.org/10.5194/egusphere-egu25-7279, 2025.
Wetlands play important roles in the ecological balance and sustainable development of arid oases. However, the interactions and feedback mechanisms in oasis hydrology–soil–vegetation systems are unclear. We conducted a 5-year field study in swamp, riparian, grassland, shrubland, and reclamation oasis wetlands to analyze the hydroclimatic processes, soil physicochemical properties, vegetation characteristics, and their interactions and feedback mechanisms in northwestern China. The precipitation was low (122.5±12.3 mm yr-1), and the differences among different wetland types were significant, with an average annual evapotranspiration of 598.2 to 654.5 mm yr-1, a groundwater depth of 85.4±5.3 to 130.1±14.8 mm), and a soil water content (SWC) of 0.26±0.03 to 0.39±0.09 v/v). Groundwater depth significantly affected SWC, pH, EC, nutrients, ions, and microbial and vegetation diversity. The differences among wetlands were significant. Reclamation for agriculture significantly increased Cl-, CO32-, Mg2+, and K+, but significantly decreased SO42-, HCO3-, Ca2+, and Na+. The overall vegetation community contained 17 families, 40 genera, and 46 species, of which dicotyledons were dominant, accounting for 56.5% of total number. Path modeling showed that groundwater depth directly affected soil water content (88%), soil ion contents (56%), and nutrient contents (32%), thereby indirectly affecting soil microbe and vegetation diversity. SWC affected vegetation diversity more strongly than groundwater depth in the wetlands, resulting in differences of vegetation diversity (total effect size, 85.3%), with a direct effect of 62.9% and an indirect effect of 23.2%. Our results show that the interactions among hydroclimatic processes, soil physicochemical properties, and human activities affect species diversity and vegetation characteristics in oasis wetlands.
How to cite: Liu, B.: Interaction process and feedback mechanisms of hydrology -soil-vegetation systems in oasis wetland, northwest China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9350, https://doi.org/10.5194/egusphere-egu25-9350, 2025.
Satellite observations provide unique opportunities for the development and evaluation of terrestrial biosphere models (TBMs). Solar-induced chlorophyll fluorescence (SIF) is one of the remotely sensed variables that is directly related to photosynthetic activity. Chlorophyll fluorescence (ChlF) is one of the pathways for the absorbed radiation within leaves, along with photochemistry and non-photochemical quenching (NPQ). However, the relationship between photosynthesis and ChlF depends on environmental conditions and on the level and saturation of NPQ. Therefore having a process-based representation of SIF within a TBM will help to fully exploit the data stream available from the remote sensing in carbon cycle studies.
We have implemented a leaf-level model of ChlF in the QUINCY ('QUantifying Interactions between terrestrial Nutrient CYcles and the climate system') TBM. Based on a previous study testing different alternatives for describing the radiative transfer of SIF, we used a radiative transfer model L2SM (developed by T. Quaife) for the SIF signal. Observed leaf level SIF spectra were used to convert the model output to observed units.
As data sources we used satellite observations of the SIF from TROPOMI as well as data products using previous satellite missions and machine learning that go further back in time, as the TROPOMI observations begin in 2018. We extracted satellite observations at the carbon dioxide (CO2) flux tower sites in different ecosystems and used these satellite SIF observations, along with gross primary production (GPP) from the flux observations to evaluate and improve our model. Since the footprints of flux towers are different from TROPOMI observations, we focus on flux towers located in homogeneous landscapes. We emphasize the use of data from research infrastructures, such as ICOS, because they have up-to-date data coverage. In addition, we used some in situ tower-based SIF observations.
According to our results, the formulation of NPQ required different parameterizations for sustained NPQ in different temperature regimes and we also tested a new formulation for NPQ in drought conditions. The magnitude of the simulated SIF signal was too high at evergreen conifer sites when compared to the in situ -observations but it was at a similar level to the satellite observations. The seasonal cycle of grassland phenology was off in the model and satellite SIF provided another data stream to work on improving it. Satellite-based SIF proved to be a useful addition for model development and having a process-based representation for SIF enhances its usefulness.
How to cite: Thum, T., Quaife, T., Duveiller, G., Honkanen, M., Lindqvist, H., Magney, T., Pierrat, Z., and Zaehle, S.: Modelling solar-induced chlorophyll fluorescence (SIF) with terrestrial biosphere model QUINCY , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14398, https://doi.org/10.5194/egusphere-egu25-14398, 2025.
Canopy structural and leaf photosynthesis parameterizations such as maximum carboxylation capacity, slope of the Ball–Berry stomatal conductance model, leaf area index, leaf chlorophyll content and canopy height are crucial for modelling plant physiological processes and canopy radiative transfer. These parameterizations also represent the largest sources of uncertainty in predictions of mass and energy exchange across ecosystems. While gradient-based inversion methods are commonly used, they often lack accuracy due to their susceptibility to becoming trapped in local minima. Stochastic approaches on the other hand alleviate this problem but they suffer the disadvantage of being computationally intensive, requiring substantial computing power to explore the full parameter space. Additionally, many process based models exhibit high nonlinearity and discontinuities, making gradient computation challenging. We propose an optimal moving window inversion framework based on genetic algorithms, using the Soil Canopy Observation Photochemistry and Energy Fluxes (SCOPE 2.0) model to constrain key ecosystem parameters. This inversion framework incorporates constraints from observed turbulent and energy fluxes, as well as net outgoing radiation and spectral reflectance, to narrow the parameter search space. Results from several ecosystems showing the advantage of this method featuring both C3 and C4 photosynthetic pathways under stressed and unstressed conditions will be presented. Further, the potential of this approach to address parameter equifinality issues commonly encountered when optimizing multiple parameters will also be discussed.
How to cite: Dutta, D. and Biswas, S.: Optimizing Ecosystem Parameterization Using Genetic Algorithm: Addressing Uncertainties and Equifinality in Modeling Plant Physiological Processes and Canopy Radiative Transfer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16276, https://doi.org/10.5194/egusphere-egu25-16276, 2025.
Accurate estimation of evapotranspiration (ET) is critical for understanding the terrestrial water and energy cycles, especially under the context of climate change and its impact on vegetation dynamics. Traditional semi-mechanistic models often struggle to accurately capture ET variability due to uncertainties in parameterizations and assumptions about vegetation responses to environmental drivers. In this study, we leverage the potential of machine learning (ML) models to improve ET estimation by integrating key biophysical and environmental variables: solar-induced chlorophyll fluorescence (SIF), photochemical reflectance index (PRI), and vapor pressure deficit (VPD). These variables provide a direct and dynamic representation of vegetation activity and environmental stress. Our results show that ML models outperform semi-mechanistic models in capturing ET dynamics across diverse spatial and temporal scales. Using explainable machine learning techniques, we further interpret the ML model's performance by identifying the relative importance of input variables and their interactions. SIF emerges as a dominant predictor, providing direct insights into photosynthetic activity and stomatal conductance. VPD is also shown to play a critical role, highlighting its influence on atmospheric demand for water. PRI contributes by offering a proxy for photoprotective mechanisms, which are crucial under stress conditions. The comparative analysis underscores the limitations of semi-mechanistic models in capturing non-linear relationships and rapid responses. Explainable ML techniques reveal that the improved performance stems from the ML model's ability to account for complex, non-linear interactions between variables and dynamically adjust to changing conditions. The findings have significant implications for hydrological modeling, water resource management, and climate change impact assessments.
How to cite: Behera, S. and Dutta, D.: From Semi-Mechanistic Model to Explainable Machine Learning: A New Approach to Evapotranspiration Estimation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16272, https://doi.org/10.5194/egusphere-egu25-16272, 2025.
Changes in heat and moisture significantly co-alter ecosystem functioning. However, knowledge on dynamics of ecosystem responses to climate change is limited. Here, we quantify long-term ecosystem sensitivity based on weighted ratios of vegetation productivity variability and multiple climate variables from satellite observations, greater values of which indicate more yields per hydrothermal condition change. Our results show ecosystem sensitivity exhibits large spatial variability and increases with the aridity index. A positive temporal trend of ecosystem sensitivity is found in 61.28% of the study area from 2001 to 2021, which is largely attributed to declining vapor pressure deficit and constrained by solar radiation. Moreover, carbon dioxide plays a dual role; which in moderation promotes fertilization effects, whereas in excess may suppress vegetation growth by triggering droughts. Our findings highlight moisture stress between land and atmosphere is one of the key prerequisites for ecosystem stability, offsetting part of the negative effects of heat.
How to cite: Hu, Y.: Ecosystems in China have become more sensitive to changes in water demand since 2001, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1136, https://doi.org/10.5194/egusphere-egu25-1136, 2025.
Fine root decomposition is essential for the cycling of carbon (C) and nutrients in terrestrial ecosystems. Although nitrogen (N) deposition is known to affect this process, the primary regulatory mechanisms remain uncertain. In this study, we investigated the impact of N addition on fine root decomposition through a three-year experiment, using two distinct N addition timelines: “Before” (fine roots collected from N addition plots and decomposed in control plots) and “During” (fine roots collected from control plots and decomposed in N addition plots). Our findings showed that N addition “Before” significantly inhibited fine root decomposition, while N addition “During” had no noticeable effect. Random forest analyses identified substrate N concentration as the key factor influencing decomposition rates. Specifically, decomposition rates were negatively correlated with N concentration and positively correlated with C:N ratios, regardless of the N addition timeline. These results support the N inhibition hypothesis and emphasize the dominant role of substrate chemistry in regulating fine root decomposition. This study offers valuable insights into ecosystem C cycling under increasing N deposition and underscores the importance of incorporating substrate chemical traits into predictive models.
How to cite: Xu, X.: Fine root decomposition in poplar plantations: Negative regulation by initial root nitrogen content, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1668, https://doi.org/10.5194/egusphere-egu25-1668, 2025.
Understory with forest floor, which constitutes the canopy structure in temperate forest, plays a significant role in carbon cycle through various mechanisms. It alters soil environmental conditions and microbial dynamics, both of which contribute to soil CO2 fluxes. By increasing carbon input to the forest floor, the understory promotes the formation of thicker litter layers, which in turn modify soil CO2 flux through direct and indirect pathways. Despite its importance, field-based studies examining the effects of understory or litter layers on soil CO2 flux, as well as how these effects vary across seasonal patterns, remain limited. In this study, we conducted both the understory experiment and the litter experiment. The understory experiment aimed to investigate changes in soil CO2 flux and various environmental factors associated with the presence or absence of understory. For this, we setup two treatment sites: one with understory (CU) and the other without understory (CO) in a temperate deciduous forest (Mt. Nam) located in Seoul, South Korea. The litter experiment was designed to evaluate the influence of litter on CO2 flux, soil temperature, and soil water content by manipulating litter depths: no litter (NL), normal litter (Con; 5.5 cm), and double litter (DL; 11 cm) in a temperate urban forest located close to the undestory experiment. Soil CO2 flux, soil temperature, and soil water content were periodically monitored in both experiments. Soil CO2 flux was consistently higher in CU than in CO across all seasons, with increases ranging from 41.9% to 130%. The largest difference was observed in winter (Dec.–Feb.), where soil CO2 flux was 0.22 g C m⁻² day⁻¹ in CO and 0.51 g C m⁻² day⁻¹ in CU. This significant difference in CU was attributed to higher soil temperature (by 0.5 C, Dec.–Feb.).Additionally, soil water content in CU was higher than in CO in all seasons except autumn (Sep.–Nov.), which could be related to deep litter layer. These results from the understory experiment can be attributed to the significantly deeper litter layer in CU compared to CO (p < 0.01). Deep litter layer could reduce the sensitivity of soil temperature to atmospheric temperature fluctuations and decrease soil water evaporation. Supporting this finding, the litter experiment demonstrated that daily mean soil water content was highest in DL followed by Con and NL. Consistently, the litter experiment showed that litter layer contributed 12.6–22.0% to the total CO2 flux from the forest floor. Intergrating the findings from both experiments, we found that the presence of understory increases annual soil CO2 flux by 60.1%. Additionally, increased litter depth influenced by understory could locally enhance the CO2 flux, contributing to the spatial dynamics of carbon cycle in the temperate forest ecosystem. Overall, our results suggest that such changes can significantly influence the dynamics of soil CO2 flux within the temperate forest carbon cycle.
How to cite: Jeong, M., Yoo, G., and Bae, J.: The Impact of Understory Presence on Soil CO2 Flux Dynamics in Temperate Forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20038, https://doi.org/10.5194/egusphere-egu25-20038, 2025.
Mountain ecosystems are highly sensitive to the impacts of climate change. Nevertheless, our knowledge of critical biogeochemical processes—key to understanding how these ecosystems cope to shifting environmental conditions—remains limited.
This study examines and compares carbon dioxide (CO2) turbulent flux measurements, obtained through the eddy covariance (EC) method at two Italian high-altitude sites: Torgnon and Nivolet in the Western Alps. These sites, part of the ICOS (Integrated Carbon Observatory System) network as Associated stations IT-Tor (Torgnon) and IT-Niv (Nivolet), are unmanaged subalpine grasslands situated at elevations of 2050 m and 2750 m, respectively, with different plant species compositions. Snow typically covers these areas from late October to late May at IT-Tor and until June at IT-Niv, restricting the growing season to approximately four to five months. Continuous EC measurements of CO2 fluxes have been conducted continuously since June 2017 at IT-Tor and since June 2019 at IT-Niv.
This work focuses on comparing CO2 fluxes from both sites under comparable meteorological conditions to explore the differences between the two canopies from an ecophysiological perspective. Additionally, phenological patterns are analyzed to evaluate how each grassland responds to extreme weather events, including the 2022 summer drought, the most severe drought event recorded in the last 17 years.
Our results emphasize the sensitivity of mountain ecosystems to climate change and highlight the importance of continuous monitoring to better understand and manage these fragile environments. The ecophysiological responses of these two mountain ecosystems to varying environmental conditions will be discussed considering their different altitude, species composition, and historical management.
Further research, combining long-term data with advanced modeling approaches, will be crucial for developing a more comprehensive understanding of how climate extremes affect mountain ecosystems across Europe.
How to cite: Vivaldo, G., Ferraris, D., Baneschi, I., Baronetti, A., Giamberini, M. S., Provenzale, A., Raco, B., and Galvagno, M.: CO2 Fluxes at high-altitude mountain ecosystems: a comparative study of two grasslands in the Aosta valley, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13663, https://doi.org/10.5194/egusphere-egu25-13663, 2025.
Mountain ecosystems are particularly sensitive to global change and are therefore often used as early warning systems while providing essential ecosystem services. For this reason, researchers aim to understand how these ecosystems develop under climate change. While focus increased in the last decades, mainly due to manipulation experiments, our understanding of how these ecosystems respond to environmental changes remains fragmented. In this study we systematically reviewed 767 manipulation experiments on global change effects in mountain environments over the past three decades, analyzing 3082 ecological responses across different organizational levels. Temperature manipulation was the most common experiment type (45% of studies), showing strong effects on plant phenology, soil respiration, and nutrient cycling. Water availability significantly impacted productivity and carbon cycling, while nutrient manipulations altered community composition and biomass production. Plant responses dominated the research (71% of studies), showing species-specific adaptations to warming. Soil microbial communities exhibited significant responses to warming, affecting decomposition processes and nutrient availability. However, critical knowledge gaps remain. Experimental studies on adult trees in tropical and boreal regions are scarce, and animal responses, biotic interactions, and aquatic environments require more attention. Furthermore, most experiments (73%) were short-term, with a duration under 5 years and focused on single factors, limiting our understanding of long-term and interactive effects. A network of standardized experiments across mountain regions, combining different research methods and collaboration between research groups, could address these gaps.
How to cite: Niedrist, G., Crepaz, H., Bottarin, R., Seeber, J., Fontana, V., Paniccia, C., Tappeiner, U., Obojes, N., Steinwandter, M., Guariento, E., Hilpold, A., and Dainese, M.: Global change experiments in mountain ecosystems: A systematic review, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14894, https://doi.org/10.5194/egusphere-egu25-14894, 2025.
Deadwood is an important and large carbon pool in unmanaged forests and will become more important in managed forests, as changes in forest management and/or more frequent disturbances will likely lead to higher deadwood amount in Central European forests. Future deadwood dynamics can be currently not accurately assessed due to lack of a conceptual understanding and data on deadwood carbon stocks, carbon fluxes, importance of fungi for deadwood decay and the habitat value of deadwood. In an upcoming 3-year project funded by the Austrian Science Fund, abbreviated with DD FOR, the project team will introduce a conceptual understanding of deadwood dynamics during its observable lifetime from deadwood creation to fragmentation and incorporation into the soil. DD FOR will utilize field experiments of deadwood decay spanning Central European temperature and precipitation gradients (~3-8 °C average annual temperature, ~700-1700 mm annual precipitation sum). The field experiments will focus on important tree species in Central Europe (e.g. Picea abies, Pinus sylvestris, Fagus sylvatica, Quercus sp.). For selected deadwood pieces we will conduct monitoring of saproxylic insects using suitable traps and quantify the fungal communities using wood samples, fruiting body inventories and state-of-the-art analytical methods, including meta bar-coding. This will establish decay rate benchmarks for fungal species, depending on climate and their host species.
We hypothesis that temperature is the main driver of deadwood decay and that moisture modulates decay with implications on fungal communities and insect habitat quality. Presence and diversity of saproxylic insects may explain variation in fungal diversity, not explained by site or stand conditions. Pilot studies suggest that (1) novel techniques are needed to quantify properties of well-decayed deadwood, including drill-resistance tools and moisture sensors, (2) deadwood position and deadwood treatment affects deadwood decay and (3) permanent plots are valuable assets and can serve as field labs for understanding deadwood dynamics. Results of DD FOR will assist deadwood-focused forest management and better consideration of deadwood in greenhouse gas reportings.
Literature
Neumann, Mathias, Sebastian Echeverria, and Hubert Hasenauer. 2023. “A Simple Concept for Estimating Deadwood Carbon in Forests.” Carbon Management 14(1):1–12. doi: 10.1080/17583004.2023.2197762.
Neumann, Mathias, Clemens Spörk, and Hubert Hasenauer. 2023. “Changes in Live and Deadwood Pools in Spruce-Fir-Beech Forests after Six Decades of Converting Age Class Management to Single-Tree Selection.” Trees, Forests and People 12(January):100382. doi: 10.1016/j.tfp.2023.100382.
Kušar, Gal, and Mathias Neumann. 2024. “Patterns of Deadwood Volume and Dynamics in Slovenian Forests.” Acta Silvae et Ligni 133:1–12. doi: 10.20315/ASetL.133.1.
How to cite: Neumann, M., Böhm, M., and Schmid, S.: Understanding interactions between deadwood decay, fungal communities and saproxylic insects based on novel field experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15673, https://doi.org/10.5194/egusphere-egu25-15673, 2025.
Forest ecosystems face considerable long-term risks in the context of escalating drought and rising temperatures. Consequently, studies examining the water balance of individual trees and entire forest stands are imperative to assess potential impacts and explore potential silvicultural strategies to mitigate the effects of climate change.
A range of methods have been employed to measure tree sapflow density (SFD), including TD (thermal dissipation), TTD (transient thermal dissipation), HRM (heat ratio method), and HFD (heat field deformation). Each method comes with advantages and disadvantages. However, when calculating the total water use of trees, two additional variables to SFD must be considered. The first is the conducting sapwood depth, and the second is the xylem sapflow profile, which represents the decrease in SFD from the outer to the inner part of the conductive sapwood. In the case of oak, the literature suggests that the conducting sapwood area/sapwood depth has primarily been determined using the light transmission method in combination with coloration due to the ring-porous properties and the formation of different colored heartwood.
In this study, the HFD method was used to measure the SFD at 1 cm intervals up to a total depth of 7.5 cm in Quercus petraea (Matt.) Liebl. (sessile oak). In addition, the sapwood depth of each tree was assessed via the light transmittance method in combination with heartwood coloring and yielded an average sapwood depth of 2.7 ± 0.6 cm for the measurement trees within a diameter range from 31.5 cm to 42.0 cm. These results are consistent with the results on sapwood depth reported in the literature for various oak species, which indicate and were interpreted with more or less zero sap flow with the beginning of the heartwood. However, the HFD data showed that xylem sapflow extended to an average depth of 5.5 cm with a steep logarithmic decline, but resulting in relative sapflow rates still around 30% at the visual axis between sapwood and heartwood.
Furthermore, both the actual measured sap flow profile and a sapwood depth-based model were used to calculate the whole tree water use. Within a range of daily water use per tree of 6 to 60 L d-1, the calculation based on the measured sap flow profile was on average 19.3 ± 0.6 % higher than with the sapwood-based profile. This daily offset of about 20 % is particularly important when calculating the water use of trees and stands under good weather conditions with high sap flow rates.
How to cite: Gebhardt, T., Hesse, B. D., Dluhosch, D., Grams, T. E. E., and Annighöfer, P.: Does visually assessed sapwood depth lead to an underestimation of whole tree water use calculations for sessile oak?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19204, https://doi.org/10.5194/egusphere-egu25-19204, 2025.
During 8 years (2015-2022), we measured net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) using eddy covariance systems in a temperate rainforest and an anthropogenic peatland in northern Patagonia (southern Chile). NEE was partitioned into gross primary production (GPP) and ecosystem respiration (Reco), while ET was partitioned into evaporation (E) and transpiration (T), which in turn were used to calculate different formulas of water use efficiency (WUE). We identified the main environmental drivers of WUE, GPP, ET, E and T. Results showed that while the forest was a consistent carbon sink (-17.82 Mg CO2 ha-1 year-1), the peatland was in average a small source (1.21 Mg CO2 ha-1 year-1). Only the expressions of WUE that included atmospheric water demand showed seasonal variation. Variations in WUE were more related to changes in ET than with changes in GPP. For both ecosystems, E increased with higher global radiation and higher surface conductance and when water table depth was closer to the soil surface. Also, higher values of E were related to higher wind speed in the forest and higher air temperature in the peatland. The absence of a close relation between ET and GPP was likely related to the dominance of plant species with low or no stomatal control. The observed increase in potential ET suggests that WUE could increase in the future in these ecosystems.
How to cite: Perez-Quezada, J., Trejo, D., Lopatin, J., Aguilera, D., Osborne, B., Galleguillos, M., Zattera, L., Celis, J. L., and Armesto, J.: Ecosystem water use efficiency in a forest and a peatland in northern Patagonia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2630, https://doi.org/10.5194/egusphere-egu25-2630, 2025.
Soil respiration (SR) is one of the largest land-atmosphere carbon fluxes. Since the industrial revolution, human activities have altered atmospheric nitrogen (N) deposition in forests, potentially affecting biotic activities and changing SR. However, this is highly uncertain, as mixed effects of N inputs on SR (i.e., increasing vs. decreasing) were observed in global forests. Here we synthesized data from global N addition experiments to quantitatively analyze how N increases or decreases SR. The revealed patterns were consistent with the observed SR changes across the natural N deposition gradient, providing a general framework to explain the diverse effects of N input on SR in global forests. Using a novel probabilistic approach, we estimated that N deposition decreased SR in 2.9% of global forests, mostly N-saturated forests in eastern China, western Europe, and eastern USA. But the net effect of N deposition increased the global forest SR budget by 5.1% (1.7 PgC yr–1). If N pollution could be effectively controlled, global forest SR and its variability would decrease, thereby reducing the uncertainty in the projected terrestrial carbon dynamics.
How to cite: Cen, X., Vitousek, P., He, N., Bond-Lamberty, B., Niu, S., Du, E., Yu, K., Zheng, M., Raich, J., Van Sundert, K., Paulus, L., He, L., Xu, L., Li, M., and Butterbach-Bahl, K.: A general framework for nitrogen deposition effects on soil respiration in global forests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4984, https://doi.org/10.5194/egusphere-egu25-4984, 2025.
Climate change has been occurring at a rapid rate and is being exacerbated by anthropogenic activities that increase global temperatures and atmospheric concentrations of greenhouse gases such as CO2. This greatly impacts ecosystems worldwide, resulting in more frequent and intense extreme weather events such as heat waves and drought. Understanding how ecosystems respond to elevated CO2 is critical for predicting the impacts of climate change on ecosystem processes, such as their ability to sequester carbon. Temperate ecosystems, in particular, are important in mitigating climate change, holding around 20% of the global plant biomass and approximately 10% of the global terrestrial carbon (Bonan, 2008). However, the capacity of these ecosystems to continue sequestering additional carbon dioxide in the future is uncertain when predicted using current terrestrial biosphere models (TBMs). To address this, improved mechanistic representations of ecosystem states and processes under changing climatic conditions are crucial, as well as the initialisation of the models using real-world observations. In this regard, ecosystem-scale experiments, such as Free-air CO2 enrichment (FACE) experiments, are extremely useful and powerful tools for improving model predictions and have frequently been used for model-data synthesis and ecosystem analysis (Walker et al, 2015).
In this study, we examined the responses of mature temperate forests to rising atmospheric CO2 and changing climatic conditions using the Ecosystem Demography model (ED2), which is a cohort-based terrestrial biosphere model (TBM). We parameterised the model with data collected from the Birmingham Institute of Forest Research, Free-air CO2 Enrichment (BIFoR FACE) experiment site. As the first study using a TBM at BIFoR, this study analysed the model’s capacity to simulate ecosystem responses to elevated CO2 (+150 ppm above ambient) and extreme weather events such as the European drought of 2022 (Gharun et al, 2024). We ran two simulations and compared model outputs against field measurements of key eco-physiological measurements such as maximum rate of carboxylation, soil moisture, and Net Primary Production (NPP). This study demonstrates the capability and the limitations of the TBM to simulate the responses of a mature temperate forest to elevated CO2 conditions under changing and extreme climatic conditions.
How to cite: Healy, S.: Modelling mature temperate forest responses to elevated CO2 and changing climatic conditions: insights from the BIFoR FACE experiment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13821, https://doi.org/10.5194/egusphere-egu25-13821, 2025.
Compound events, such as the co-occurrence of heat and drought, have increasingly impacted European forests in recent years, though with a large spatial variability. To date, we still lack a mechanistic understanding of the complex interactions in the soil-plant-atmosphere system at different spatiotemporal scales, which drive the response of ecosystems and the tree individuals therein to stressors, such as heat or drought. Currently, there is a lack of appropriate measurement, data and modelling tools to fully capture relevant processes and their dynamics at different spatiotemporal scales in real time, especially at remote sites with limited access or power availability. Thus, there is an urgent need for novel sensor networks, which are mobile, easy deployable, cost-efficient and energy autonomous. At the interface of environmental and engineering science, the interdisciplinary project ECOSENSE (Werner et al. 2024) tackles these challenges to develop a new versatile, distributed and intelligent sensor network to measure carbon and water fluxes and stress responses (such as volatile organic compounds (VOCs) and chlorophyll fluorescence) at high temporal dynamics in forests. With this new ECOSENSE Toolkit, we will open new opportunities for a rapid assessment of spatiotemporal ecosystem processes in the face of climate change.
The ECOSENSE Toolkit is currently being developed and tested in a mixed European Beech and Douglas Fir forest in SW-Germany with three canopy access towers and an eddy covariance system at 46 m height. Continuous measurements of CO2, H2O and VOC fluxes from soils, stems, leaves and atmosphere are conducted at different spatiotemporal scales since March 2024. Additionally, stress responses are captured by leaf and remotely sensed chlorophyll fluorescence. Novel sensors and sensor networks are continuously developed, tested, and finally integrated into the existing measurement infrastructure, such as a novel, light-weight cuvette for continuous leaf-level gas exchange and volatile organic compound emission measurements.
Reference:
Werner C, Wallrabe U, Christen A, Comella L, Dormann C, Göritz A, Grote R, Haberstroh S, Jouda M, Kiese R, Koch B, Korvink J, Kreuzwieser J, Lang F, Müller J, Prucker O, Reiterer A, Rühe J, Rupitsch S, Schack-Kirchner H, Schmitt K, Stobbe N, Weiler M, Woias P, Wöllenstein J (2024). ECOSENSE - Multi-scale quantification and modelling of spatio-temporal dynamics of ecosystem processes by smart autonomous sensor networks. Research Ideas and Outcomes 10: e129357. https://doi.org/10.3897/rio.10.e129357
How to cite: Werner, C., Haberstroh, S., and Wallrabe, U. and the ECOSENSE Team: ECOSENSE: Assessment of spatiotemporal dynamics in ecosystem processes and fluxes by smart autonomous sensor networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16670, https://doi.org/10.5194/egusphere-egu25-16670, 2025.
Ecosystem productivity and carbon uptake in the circumpolar boreal forest are contingent on available nitrogen, which ultimately originates from inputs via deposition and biological nitrogen fixation. Nitrogen deposition rates in boreal forests are relatively small compared to other biomes, and most biological nitrogen fixation research has focused on moss-diazotroph associations. However, the relative contributions of these two primary nitrogen inputs to ecosystem nitrogen stocks have not been widely investigated. In this study, we combined a mass balance approach and literature synthesis to estimate rates of nitrogen accumulation and nitrogen inputs across a network of 18 wildfire chronosequences spanning the boreal biome. We found that nitrogen accumulation rates were strongly linked with fire regime (stand-replacing versus surface fires) and canopy dominance (deciduous versus evergreen canopies). Furthermore, a considerable amount of accumulating nitrogen in these boreal forests was unexplained by the known inputs estimated from the literature synthesis, particularly in forests with stand-replacing fire regimes and more deciduous tree cover that together had the highest nitrogen accumulation rates. This unexplained fraction of nitrogen inputs in some forests may originate from poorly quantified niches of biological nitrogen fixation. Exploring this research frontier will help improve predictions of boreal forest nitrogen cycling and carbon uptake in changing climate and wildfire regimes.
How to cite: Hupperts, S. F., Berninger, F., Chen, H. Y., Fenton, N., Jean, M., Köster, K., Larjavaara, M., Mack, M. C., Nilsson, M.-C., Palviainen, M., Prokushkin, A., Pumpanen, J., Seedre, M., Simard, M., and Gundale, M. J.: A network of 18 wildfire chronosequences reveals key drivers of the boreal nitrogen balance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1374, https://doi.org/10.5194/egusphere-egu25-1374, 2025.
